STP PipeWrap CT 337
Hot-applied coal tar enamel tape reinforced with glass-fibre fabric, built to shield buried and immersed steel pipelines against aggressive soil corrosion for the long haul.
What is it?
A heavy-grade, hot-applied anti-corrosion wrapping tape made of coal tar enamel sandwiching a high-tensile glass-fibre carrier, torch-fused onto primed steel pipe.
Where is it used?
External protection of buried and immersed steel pipelines: drinking water, raw water and firefighting mains, thermal-plant lines, and oil and gas pipelines in corrosive soils.
Why use it?
It forms a continuous, moisture-resistant, dielectric barrier that isolates the steel from soil and groundwater, working alongside cathodic protection to extend pipeline life.
How is it applied?
Blast the pipe to SA 2½, prime with ShaliPrime PW CT, torch the tape glossy and wrap it spirally with a minimum 12 mm overlap under firm tension.
About STP PipeWrap CT 337
STP PipeWrap CT 337 is the heavier grade in STP Limited’s hot-applied coal tar tape range, engineered for external corrosion protection of steel pipelines that spend their working life underground or submerged. Each tape is built from a specially formulated coal tar enamel that encases a high-tensile glass-fibre fabric, giving it both the chemical inertness of coal tar and the mechanical toughness of a reinforced carrier. A thin polythene film on either face keeps the roll from sticking to itself and peels away cleanly at the point of application. Compared with the lighter CT 221, the 337 grade delivers a greater film build and more mechanical protection, which is why specifiers reach for it on larger-diameter mains and lines laid through rocky or abrasive backfill.
For contractors across Delhi NCR and pan-India, the appeal of this system is that it does two jobs at once. The coal tar barrier keeps water, dissolved salts and soil chemicals off the steel, while the glass-fibre reinforcement resists the impact and shear a pipe sees during lowering, backfilling and thermal movement. Because it is torch-fused rather than cold-wrapped, the enamel flows into every surface irregularity and bonds intimately to the primer, leaving no air pockets for corrosion to start. The result is a coating that behaves as a dielectric shield, complementing an impressed-current or sacrificial-anode cathodic protection scheme rather than fighting it. Space Arc Engineering supplies CT 337 with the matching primer, thickness guidance and on-site applicator support that a first-time crew usually needs.
The technical insight
Buried steel corrodes because soil is an electrolyte: moisture, oxygen and dissolved salts complete a circuit that lets iron give up electrons and rust away, often fastest at coating defects called holidays. PipeWrap CT 337 breaks that circuit in two ways. First, the coal tar enamel is naturally hydrophobic and chemically stable, so it physically excludes the water and ions the reaction needs. Second, and just as important, it is a good electrical insulator, which is why the datasheet quotes a holiday-test withstand of 15 kV for the 4 mm tape and passes a cathodic disbondment test with less than 5 mm undercutting from a deliberate 6 mm holiday. That dielectric strength is what lets the coating live in harmony with cathodic protection: a well-insulated pipe draws very little protective current, so the CP system only has to guard the tiny areas where the coating is damaged. The glass-fibre carrier carries the tensile load, holding the enamel in place while the softening point of up to 121 degrees C keeps it stable at service temperatures, and the low-temperature cracking test at minus 23.3 degrees C confirms it stays intact through thermal cycling. Hot application is the final piece: torching the tape until it turns glossy lets the enamel wet the primed steel and fuse each spiral overlap into a single monolithic sleeve.
Where it is used
- External anti-corrosion wrapping of buried steel drinking-water and raw-water transmission mains
- Firefighting and hydrant pipeline networks in industrial and institutional projects
- Raw-water and cooling-water lines in thermal power plants
- Oil, gas and other hydrocarbon pipelines routed through corrosive soils
- Protection of immersed pipes, fittings and appurtenances in aggressive water
- Field coating of welded joints and appurtenances left bare during pipe laying
- In-situ refurbishment and repair of ageing or partially corroded pipelines
- Coating of specials, bends and valve bodies where factory coatings cannot reach
Key advantages
- Heavier grade than CT 221, giving greater film build and mechanical protection
- Coal tar enamel barrier resists moisture, soil chemicals and bacterial growth
- High dielectric strength works in tandem with cathodic protection schemes
- Glass-fibre reinforcement withstands impact, shear and thermal movement
- Torch-fused overlaps form a continuous, pocket-free monolithic sleeve
- Available in 2, 3 and 4 mm thickness to match soil aggressiveness and pipe size
- Well suited to in-situ repair and refurbishment of existing pipelines
- Wide climatic tolerance with stable performance from sub-zero to elevated service temperatures
Limitations & considerations
- Hot application requires a butane torch and a trained crew, so it is slower and more skill-dependent than cold-applied tapes
- Steel must be blast-cleaned to SA 2½ and primed with ShaliPrime PW CT; poor surface prep is the most common cause of disbondment
- As a coal tar product it demands proper ventilation, PPE and care to avoid skin, eye and vapour contact during application
- Not a stand-alone corrosion solution on cathodically protected lines; it is designed to work with, not replace, a CP system
- Torch heat and open flame make it unsuitable near live gas or in confined spaces without a hot-work permit
- Rolls have a 12-month shelf life and must be stored under shed, away from heat, stacked no more than three high
Selection & best practice
Success with CT 337 is decided at the surface. Blast the pipe to SA 2½ (Swedish standard) to strip mill scale, rust, oil and grease, then apply ShaliPrime PW CT at 100 to 120 ml per square metre to reach a dry film of about 30 microns, and let it touch-dry for 5 to 15 minutes. Leave roughly 200 mm bare at each pipe end so field welds and hydro-testing can be completed first, then coat those gaps at site. Peel the PE film and pass a butane torch over the tape until it turns glossy-smooth before laying it onto the primer. Wrap spirally under firm, even tension with a minimum 12 mm overlap, keeping the tape joint facing downward on the outside of the lap so water cannot track in, and press out every air pocket and bridge. Finish with a holiday (spark) test at the datasheet voltage for the chosen thickness before lowering the pipe, and time the whole operation to coincide with erection and lowering into the trench to avoid handling damage.
Specifications
| Product type | Hot-applied anti-corrosive coal tar tape (heavy grade) |
| Composition | Coal tar enamel sandwiching high-tensile glass-fibre fabric, PE film both faces |
| Softening point | 65 to 121 degrees C |
| Penetration (25 C, 100 g, 5 sec) | 1 to 9 |
| Service temperature | Up to 60 degrees C |
| Holiday test voltage | 10 kV (2 mm), 12 kV (3 mm), 15 kV (4 mm) |
| Low-temperature cracking | No cracking at minus 23.3 degrees C |
| Recommended primer | ShaliPrime PW CT at 100 to 120 ml/m2 (approx. 30 micron DFT) |
| Minimum overlap | 12 mm between adjoining layers |
| Available sizes | 2 mm (20 m rolls), 3 & 4 mm (10 m rolls); widths 200/250/333/500/1000 mm |
| Shelf life | 12 months in original condition, stored under shed away from heat |
Industry use cases
Water Utilities & Municipal
Wrapping buried MS transmission and distribution mains carrying drinking or raw water through corrosive urban and rural soils.
Power Generation
Protecting raw-water, cooling-water and firefighting lines in thermal power plants where lines run underground across the plant.
Oil & Gas
External corrosion protection of buried hydrocarbon pipelines and field joints, complementing the pipeline’s cathodic protection system.
Industrial Firefighting Networks
Coating hydrant ring mains and firewater loops in factories, refineries and warehouses that are laid below grade.
Pipeline Rehabilitation
In-situ recoating of ageing or partially corroded pipelines during shutdowns, restoring the dielectric barrier without full replacement.
Frequently asked questions
What is the difference between PipeWrap CT 337 and CT 221?
Which primer should I use and how much?
Does this tape replace cathodic protection?
What thickness and width should I order?
How is the tape applied on site?
What safety precautions are needed?
How we position STP PipeWrap CT 337
Within the STP range, choose CT 337 when you need a heavier, more mechanically robust coating than STP PipeWrap CT 221; pair it with its dedicated ShaliPrime PW CT primer for a warranted bond. Where a bitumen-based system is preferred over coal tar, STP PipeWrap BT is the sister product using the same hot-applied wrapping technique. For above-ground concrete and structural surfaces on the same project, our Fosroc protective-coatings line (Dekguard and Nitocote) and Sika anti-carbonation coatings cover a different exposure that pipe wrap does not address. Space Arc supplies the tape, primer, torch consumables and applicator support as a single package across Delhi NCR and pan-India.
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